https://bugs.kde.org/show_bug.cgi?id=527566
Bug ID: 527566
Summary: Intel-primary: stale trailing on NVIDIA-connected DP
output in KWin 6.8.1; NVIDIA-primary avoids it
Classification: Plasma
Product: kwin
Version First 6.8.1
Reported In:
Platform: Garuda Linux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: platform-drm
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Target Milestone: ---
DESCRIPTION
With Intel as KWin's render GPU, moving windows leaves stale trails on the
right-hand monitor connected to NVIDIA. The Intel-connected laptop and
left-hand displays look normal. Spectacle recordings do not show the corruption
visible on the physical display.
STEPS TO REPRODUCE
1. Use Plasma Wayland with Intel Tiger Lake UHD and NVIDIA RTX 3060 Laptop,
with this topology:
- NVIDIA (PCI 0000:01:00.0, card1): right DP-1, 60 Hz.
- Intel i915 (PCI 0000:00:02.0, card2): laptop eDP-2, 240 Hz; left DP-3, 60
Hz.
All three outputs use scale 1.1 in the current session.
2. Start a session rendering on Intel (supportInformation reported Mesa Intel
UHD, OpenGL ES).
3. Move/interact with windows on DP-1 and observe the physical monitor.
OBSERVED RESULT
Stale trailing/ghosting on DP-1. The affected session's journal contains:
Atomic commit failed: EBUSY
Failed to allocate a graphics buffer for a swapchain
These messages establish occurrence, not a confirmed causal relationship.
EXPECTED RESULT
Correct updates on all three monitors with Intel rendering.
WORKAROUND TESTED
Create ~/.config/plasma-workspace/env/kwin-gpu-order.sh containing:
#!/bin/sh
export KWIN_DRM_DEVICES=/dev/dri/card1:/dev/dri/card2
Then log out and back into Plasma Wayland. This selects NVIDIA first on this
machine and eliminated the visible corruption. Current supportInformation
confirms NVIDIA OpenGL ES rendering and all three outputs enabled. No
swapchain-allocation or EBUSY messages appear in the subsequent sessions
checked today.
For others: identify your own GPU-to-card mapping first; card numbers can
differ or change across boots. This is a workaround, not a confirmed root-cause
fix.
SOFTWARE
Garuda Linux; kwin/plasma-desktop 6.8.1-1; Qt 6.12.0; kernel 7.3.0-2-garuda;
nvidia-utils and nvidia-open-dkms 615.78.08-1; Mesa 26.2.5; vulkan-intel
installed. Current vulkaninfo lists both hardware GPUs.
RELATED REPORTS / LIMITS
527251 is a duplicate of 527163, but the original report primarily concerns
NVIDIA rendering to an Intel-connected display. This case fails with Intel
rendering to the NVIDIA-connected output. The host-memory guard from commit
54288bdf is already present in upstream v6.8.1. 527184 concerns
brightness/gamma flicker and is a duplicate of 523237.
No source-level root cause or bisected regression commit is established here.
The previous investigation included a KWIN_DISABLE_VULKAN setting, but its
effective runtime state in the failing session was not captured. The working
override has been preserved; a controlled retest and failing-session
diagnostics remain to be collected.
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